Introduction: There is mounting evidence that the time of breast cancer diagnosis and the start of treatment can improve survival rates. The aim of this study was to test the relationship between the season of breast cancer diagnosis and the survival of women patients receiving standard surgery treatment with radiotherapy.
Materials and methods: The nonmetastatic breast cancer patients (n = 991) were followed from the date of diagnosis until death. Cox proportional hazards models were used to calculate multivariate hazard ratios (HRs) for all-cause mortality. HRs and 95% confidence intervals (CIs) were estimated in models adjusted for clinicopathologic and treatment factors.
Results: After adjusting for independent prognostic variables, we found that patients diagnosed in summer and autumn had a 40% reduced risk for 0-3-year mortality when compared to those diagnosed in spring. Among women aged <50 years, HRs comparing autumn with spring diagnosis categories were 0.53 (95% CI: 0.31-0.91) for 0-5-years and 0.68 (95% CI: 0.46-0.89) for 5-10-years after diagnosis. Diagnosis in autumn was associated with improving survival in younger patients treated with adjuvant chemotherapy (HR = 0.61, 95% CI: 0.39-0.96, P = 0.003).
Conclusions: The diagnosis in summer and autumn was associated with a better overall prognosis. The effect of season of diagnosis on survival rate was most pronounced in the young age patients receiving chemotherapy.
Keywords: Breast cancer; Vitamin D; season of diagnosis; survival.